Known gas turbine engines generally include rows of circumferentially spaced nozzles and buckets. A turbine bucket generally includes an airfoil having a pressure side and a suction side and extending radially upward from a platform. A hollow shank portion may extend radially downward from the platform and may include a dovetail and the like so as to secure the turbine bucket to a turbine wheel. The platform generally defines an inner boundary for the hot combustion gasses flowing through a gas path.
Various types of cooling schemes have been used to keep the components of the turbine bucket within operational ranges so as to promote component lifetime. These cooling schemes, however, may promote localized regions of temperature differentials that may lead to thermally induced strain. For example, an airfoil may have a number of internal ribs with internal cooling holes therethrough for the passage of a cooling medium. One such rib may be positioned about the leading edge of the airfoil so as to provide the cooling medium via the internal cooling holes for impingement cooling. The internal rib thus may be highly cooled by the cooling medium but connected to the relatively hot airfoil walls. Such a high temperature differential therein may cause a thermal strain to develop in the internal rib. This strain may be amplified by stress concentration factors associated with the internal cooling holes such that the stress may impact on component lifetime. Although attempts have been made to control the temperature differentials, temperature control techniques generally require additional cooling flows at the expense of engine efficiency.
There is thus a desire for an improved turbine bucket for use with a gas turbine engine. Preferably such a turbine bucket may have an airfoil that may limit the internal stresses caused by a temperature differential therein without excessive manufacturing and operating costs and without excessive cooling medium losses for efficient operation and an extended component lifetime.